An important aspect when designing a combustion chamber or cylinder and its associated ports is the production of an effective in-chamber motion field in the form of an axial eddy known as “swirl”. An efficient design produces a high swirl to enable a quick distribution of the air or air/fuel mixture in the chamber which leads to efficient combustion.
Another design criterion is the discharge coefficient, a measure of mass flow rates from a port, or the permeability of the chamber, which represents the efficiency with which the intake ports fill the chamber with air or air/fuel mixture. This is also known as engine breathing.
In known four cylinder engines, volumetric efficiency is increased by providing two intake ports or ducts for each cylinder. The design of the ducts is different. One is configured to have a high swirl value and the other is configured to have a high level of permeability. A problem with such an arrangement is that the port with high permeability provides an opposite swirl vortex leading to a reduction in the overall swirl value. One previously proposed solution is the installation of a swirl flap adjacent to a port in order to produce the desired swirl value and thus the desired combination efficiency. However, the use of a swirl flap necessarily leads to a loss of volumetric efficiency.
Therefore, it is desirable to seek to provide an improved in-chamber motion, and provide an intake arrangement with improved volumetric efficiency. In addition, other desirable features and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.